VICI 235 Dynacalibrator - Manual (Page 29)

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9. Rinse the fan screen and fan filter in clean water and blow dry with low-
velocity air.
10. Reinstall the fan, fan filter, fan screen brackets, and fan screen using the four
screws, lockwashers, and hex nuts.
11. Replace the top cover of the unit and return it to service according to the
procedures on page 10.
Dilution Flowmeter Calibration
VICI recommends that Dynacalibrators be returned to the factory for NIST-trace-
able flow certifications, unless you have access to sophisticated flow measuring
equipment.
Chamber Temperature Calibration
Prior to shipment, the permeation chamber digital temperature control is
calibrated against the temperature of the gas in the permeation chamber using
an NIST-traceable PRT, (platinum resistance thermometer). The results of this
calibration have been supplied with your instrument.
At this point, it is helpful to give an overview of the total calibration process.
A multiple point measurement is made with excursions to the extremes of range.
The values logged during this process allow a calculation of correction that gives
very tight agreement between the measured and the setpoint values. This cali-
bration equation is downloaded into the control board, correcting the temperature
output values to be within the tolerances of the controller.
In point of definition, measured temperatures are the equilibrium temperatures
that result at specific temperature setpoints. Calibration is done by running
multiple setpoints to characterize the response of the controller and oven. This
characterization is then modeled and corrections are calculated based on the
model response. The corrections are input and then the multiple setpoints are
again run with the PRT, and must fall within the specification in order to move
to final assembly. To define this process further is outside of the scope of this
document and the range of work that is done by field services.
Calibration temperatures are integral Celsius temperatures (±0.1°C) that will
exist in the permeation chamber at specific digital settings. These temperatures
are always expressed in integers, since all permeation device calibrations are
performed at integral Celsius temperatures. Dynacalibrator calibration tempera-
tures are NIST-traceable to match permeation device calibrations which are also
NIST-traceable.
Recalibration of all points is normally not required nor indicated. Recertifica-
tion on an annual basis is recommended at the temperature setpoints where
permeation devices will be used. Example: If an h
2
S permeation device is going
to be used at 55°C, and a COS tube is being used at 40°C, then the recertification
should be done at 2 points, 55°C and 40°C. This reduces the cost of recertification
and cuts down considerably on the time in test.
Maintenance